Control system for active attenuation of torque-steer via electric power steering

ABSTRACT

The present invention provides a device for dynamically counteracting torque steer which includes a processor adapted to calculate a correction factor from a calculated axle torque on front wheel drive half shafts of the vehicle. A power circuit is provided responsive to the calculated correction factor to provide an offset current through the power steering unit or the braking system of the vehicle to counteract the torque steer.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a torque steercorrection device, and more particularly, the present invention relatesto a torque steer correction device that compensates for torque steercaused by vehicle powertrain torque.

BACKGROUND

[0002] Front wheel drive vehicles commonly undergo a phenomenon known astorque steer. Torque steer is a vehicle's desire to turn left or rightduring acceleration. The causes for torque steer are numerous. However,these causes are rooted in the component architecture of the front wheeldrive vehicle.

[0003] In front wheel drive vehicles, the power plant which drives thevehicle is operationally engaged to the front wheels. The power plantdrives a transaxle which in-turn drives half shafts that extend betweenthe transmission and the vehicle's front wheels. Each half shaft extendsfrom one portion of the transmission to a corresponding wheel. Dependingon the lateral and angular location of the transmission with respect tothe vehicle, each half shaft commonly has a different length and anglethan the other. The difference in length and angle of one half shaftfrom the other creates a moment arm about the steering axis of thevehicle. As a result, when the vehicle is accelerated, the rotationaltorque applied to the half shafts causes the vehicle to steer. Thiseffect creates an unintended tendency for the vehicle to steer, which isundesirable for a vehicle driver. Numerous other causes for a vehicletorque steer also exist such as asymmetric tire slip. The presentinvention was developed in light of these and other drawbacks.

SUMMARY OF THE INVENTION

[0004] The present invention addresses these and other drawbacks byproviding a device for using the power steering unit to counteracttorque steer. The present invention provides a processor that isresponsive to vehicle parameters to calculate axle torque at half shaftsof the front-wheel drive vehicle. The processor includes a look-up tableto associate a correction factor with the calculated torque to determinean amount of torque to be applied by the power steering unit to offsetthe torque steer. In the case of power steering, a power circuitsupplies the required offset current to the power steering unit todynamically offset the torque through the vehicle. In the case of adifferential braking system, the brake system adjusts the individualbrakes to offset the torque steer.

[0005] In a further aspect, a method is provided for counteractingtorque steer which includes reading a plurality of engines parameters,calculating an axle torque at each of the pair of half shafts of a frontwheel drive vehicle, determining a correction factor from the calculatedaxle torque, and applying a counteracting torque by the power steeringunit to the steering linkage of the vehicle or with a differentialbraking system to counteract torque steer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a schematic view of a front-wheel drive vehicle with atorque steer correction device according to the present invention;

[0007]FIG. 2 is a schematic view of a central processing unit utilizinga torque steer correction device according to the present invention; and

[0008]FIG. 3 is a flow chart depicting the operation of a torque steercorrection device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Referring now to FIG. 1, a vehicle 10 is shown having torquesteer attenuation device according to the present invention. Vehicle 10is a front wheel drive vehicle having an engine 12, transaxle 14,steering linkage 16, half shafts 18A and 18B, wheels 20A and 20B, powersteering unit (PSU) 22, steering wheel 24, central processing unit (CPU)26, and brake system 21 that controls brakes 23A and 23B.

[0010] Engine 12 is preferably a gas powered conventional engine whichacts as the power plant for the vehicle 10. The energy output of engine12 is supplied to the transaxle 14 which, in turn, modifies the engineoutput according to desired torque and speed characteristics by shiftingbetween a plurality of gears. The modified output from transaxle 14 isthen supplied to each half shaft 18A and 18B. Half shafts 18A and 18Bthen supply the rotational output from transaxle 14 to respective wheels20A and 20B.

[0011] Power steering unit (PSU) 22 is an electric motor system whichderives its power from either a vehicle battery or the alternatorcircuitry of vehicle 10 (not shown). The power steering unit PSU 22 isoperationally engaged to steering linkage 16 to cause rotation of eachwheel 20A and 20B about their steering axes. PSU 22 provides motorassistance to the steering linkage 16 of the vehicle 10 responsive toinput from the steering wheel 24 to assist the vehicle driver in turningthe vehicle steering wheel.

[0012] With continued reference to FIGS. 1 and 2, CPU 26 receivesvarious inputs from vehicle 10 including manifold pressure from manifoldpressure sensor 28, engine speed and vehicle speed from sensors 30, andthe current gear of transaxle 14 from gear sensor 32. Additionally, CPU26 preferably receives inputs from conventional differential breakingsensors used in conjunction with a differential braking system, which issometimes used as a steering system on a vehicle, as is known to oneskilled in the art. Specifically, a yaw gyro sensor 31 indicates therotational velocity or acceleration component of the vehicle, a steeringwheel turn angle sensor 33 indicates the turn position of the steeringwheel or steering linkage 16, an accelerometer sensor 35 indicates theacceleration of the vehicle, and individual wheel speed sensors 37indicate the individual wheel speeds of all vehicle wheels.

[0013] In a first embodiment, as described with respect to FIG. 2, CPU26 includes a processor 42 adapted to calculate the output torque onhalf shafts 20A and 20B supplied from transaxle 14. CPU 26 also includesa look-up table 44 which correlates a plurality of different motorcorrections to a respective one of a plurality of correction factors. Inthe present embodiment, the correction factor is the required torque orsome value representative of the required torque for offsetting thetorque steer at that respective axle torque. Preferably, look-up table44 is generated by experimental data whereby the torque steer specificto each given vehicle is determined across a range of output torques.However, the motor correction for the torque steer can also becalculated by the CPU 26, eliminating the lookup table. This calculationuses known design information, such as half-shaft length and otherrelevant architecture, in combination with the read in parameters frommanifold pressure from manifold pressure sensor 28, engine speed andvehicle speed from sensors 30, and the current gear of transaxle 14 fromgear sensor 32 to calculate the torque. Additionally, any combination orsubcombination of these factors can be used to determine the torquesteer. In another instance, the correction factors can be calculated,without use of experimental information, and then listed in a lookuptable fashion. Other modifications are also possible without deviatingfrom the scope of the claimed invention.

[0014] Power circuit 46 electrically communicates with both CPU 26 andPSU 22. Power circuit 46 outputs a specific current to PSU 22 inresponse to the motor correction generated from central processing unit26 in response to the axle torque of look-up table 44.

[0015] When a conventional front wheel drive vehicle, such as vehicle 10accelerates, torque steer causes wheels 20 and steering wheel 24 toturn. The present invention counters this unintended turning bysupplying a torque (but not necessarily steering wheel displacement) inthe opposite direction to the torque steer with power steering unit 22.This is accomplished by the steps set out in FIG. 3. Here, in step 48,engine parameters such as axle speed 34, manifold pressure 36, enginespeed 38, and current gear 40 are read into the processing unit 36. Instep 50, the axle torque on half shafts 18A and 18B are calculated inprocessor 42. However, it is understood that other means of calculatingaxle torque can be effectuated and the present invention is not limitedto that disclosed herein. For instance, an acceleration sensor can beused in combination with a grade sensor to calculate the desired torque.In another instance, look-up tables can be provided for each of the readparameter to thereby to determine the output torque. Moreover, theengine parameters can be directly indexed to the correction factor,bypassing the torque calculation, to determine the output torque. Othersimilar methods can be used to determine the correction factor.

[0016] In step 52, the calculated axle torque is then compared on thelook-up table to determine the desired correction factor to offset thetorque steer for the given axle torque. When the correction factor isidentified for a given axle torque, a signal representative of thecorrection factor is output to the power circuit 46. Power circuit 46then routes the appropriate current through PSU 22 to provide therequired counter torque to the steering linkage 16 to counteract thetorque steer in the steering linkage 16 and wheels 20A and 20B in step54.

[0017] In another aspect of the present invention, a conventionaldifferential braking system is used to offset the torque steer of thevehicle. As is known in the art, differential braking systems utilizethe application of pressure on each independent brake, such as any oneof brakes 23A and 23B as well as the not shown rear brakes, to controlthe yaw or turning behavior of the vehicle. Accordingly, with referenceto FIG. 2, the correction factors are representative of a correctionsignal sent to the braking system 21 to adjust pressure to brakes 23Aand 23B to offset the calculated torque steer.

[0018] The operation of the preferred embodiment is described withcontinued reference to FIG. 3. In step 48, the engine parameters such asaxle speed 34, manifold pressure 36, engine speed 38, and current gear40 are read into the processing unit 36 are read in for calculation ofdifferential axle torque. Additionally, information from yaw gyro sensor31, steering wheel turn angle sensor 33, accelerometer sensor 35,individual wheel speed sensors 37 are read in for operation of thedifferential braking system. In step 50, the axle torque on half shafts18A and 18B are calculated in processor 42. As in the previousembodiment, it is understood that other means of calculating axle torquecan be effectuated and the present invention is not limited to thatdisclosed herein. In step 52, the calculated axle torque is thencompared on the look-up table to determine the desired correction factorto offset the torque steer for the given axle torque. When thecorrection factor is identified for a given axle torque, a signalrepresentative of the correction factor is output to the braking system21 to apply pressure to brakes 23A and 23B as well as the remainingbrakes, if needed, to offset the torque steer of the vehicle in step 54.

1. A device for countering torque steer of a vehicle, the devicecomprising: a control unit operationally engaged with a steering systemon the vehicle to offset a torque steer applied to the steering system;and a processor responsive to at least one parameter read from at leastone vehicle sensor to determine a correction factor based on the atleast one parameter, the correction factor representative of anadjustment required by the control unit to offset the torque steerapplied to the steering system; wherein the control unit is responsiveto a correction signal output from the processor to cause the controlunit to counter the torque steer of the vehicle, wherein the correctionsignal is based on the correction factor.
 2. The device according toclaim 1, further comprising: a transaxle; a set of wheels; a set ofshafts operationally engaged with the set of wheels and the transaxle tosupply rotational energy from the transaxle to the set of wheels,wherein the processor is adapted to: calculate an axle torque on the setof shafts responsive to the at least one parameter; and determine thecorrection factor from the calculated axle torque.
 3. The deviceaccording to claim 2, wherein the processor includes a look-up table,wherein the processor is adapted to select the correction factor fromthe look-up table based on the calculated axle torque.
 4. The deviceaccording to claim 2, wherein the at least one parameter includes amanifold pressure, a current gear of the transaxle, and an axle speed ofthe set of shafts.
 5. The device according to claim 1, wherein thecontrol unit is a power steering unit.
 6. The device according to claim1, wherein the control unit is a differential braking system.
 7. Avehicle comprising: a power plant; a pair of wheels; a transaxlereceiving rotational energy from the power plant; a pair of shafts, eachof the pair of shafts extending from the transaxle to a respective oneof the pair of wheels; a steering system for turning the pair of wheelsto cause turning of the vehicle; a torque steer countering deviceincluding: a processor responsive to at least one parameter suppliedfrom at least one vehicle sensor to determine a correction factor basedon the at least one parameter; and a control unit responsive to acorrection signal output from the processor to counter a torque steer ofthe steering system, wherein the correction signal is based on thecorrection factor.
 8. The vehicle according to claim 7, where in theprocessor is adapted to: calculate an axle torque on the pair of shaftsin response to the at least one parameter; and determine the correctionfactor from the calculated axle torque.
 9. The vehicle according toclaim 8, wherein the processor includes a look-up table, wherein theprocessor is adapted to select the correction factor from the look-uptable based on the calculated axle torque.
 10. The vehicle according toclaim 8, wherein: the at least one parameter includes a manifoldpressure, a current gear of the transaxle, and an axle speed of the pairof shafts.
 11. The vehicle according to claim 7, wherein the controlunit is a power steering unit.
 12. The vehicle according to claim 7,wherein the control unit is a differential braking system.
 13. A devicefor countering torque steer comprising: a control unit engaged to asteering system to counter the torque steer; and a processor including alook-up table, the processor responsive to a manifold pressure, acurrent gear of a transaxle, and an axle speed of a pair of half shaftsof the vehicle to calculate an axle torque on a pair of half shafts, theprocessor adapted to determine a correction factor based on thecalculated axle torque on the pair of half shafts; wherein the controlunit counteracts torque steer based on a signal from the processorrepresentative of the correction factor.
 14. A method for counteractingtorque steer of a vehicle, the method comprising the steps of: readingat least one engine parameter from at least one sensor in the vehicle;determining a correction factor based on the at least one engineparameter which is sufficient to counteract the torque steer; andapplying a correction torque to a steering system of the vehicle basedon the determined correction factor, wherein the correction torque issufficient to counteract the torque steer.
 15. The method according toclaim 14, further comprising a processor having a look-up table, theprocessor adapted to determine the correction factor from the look-uptable.
 16. The method according to claim 14, wherein the at least oneengine parameter includes a manifold pressure, a current gear of atransaxle, and an axle speed.
 17. The method according to claim 14,wherein the correction torque is applied by a differential brakingsystem.
 18. The method according to claim 14, wherein the correctiontorque is applied by a power steering unit.